Stabilized hydrocarbon oil



Patented May 14, 1935 2,001,108 STABILIZED nrpnocsnnon on.

Charles K. Parker, Richmond, CaliL, assignor to Standard Oil Company of California, San Francisco, Calif., a corporation of Delaware No Drawing. Application July 6, 1931, Serial No. 549,085

8 Claims.

This invention relates to a hydrocarbon oil such as a petroleum oil particularly adapted for use as a lubricating oil, a transformer oil, or an electric switch oil, the hydrocarbon or petroleum oils of this invention being characterized by their stability and resistance to change in color or deterioration when exposed-to light and/or air.

The invention also relates to the use of par ticular naphthenic compounds adapted to stabilize petroleum oils for the purposes, stated hereinabove.

This invention also relates to a mode of preparing certain naphthenic compounds which are particularly effective, when properly admixed with a suitable petroleum oil, in inhibiting and preventing the deterioration of such petroleum oils.

Refined petroleum lubricating and transformer oils suffer a marked deterioration when exposed to light and/or air. Generally, such petroleum oils darken in color and eventually become saturated with and deposit a finely divided oil-insoluble carbonaceous material commonly known as sludge. The rapidity of this deterioration varies with various oils and depends upon their source and refinement as well as upon the conditions to which they are exposed. The deterioration appears to take place slowly in the dark but becomes rapid when the oil is subjected to light. When oils are exposed both to light and air, even highly refined oils have been known to deposit an insoluble sludge in a period of time varying from a few hours to a few days. It will be evident that transformer and switch oils containing a carbonaceous material or sludge therein are unsatisfactory for the purpose for which they are designed andmarked changes occur in the dielectric strength of such oils upon deterioration of the character referred to hereinabove.

The nature of the changes which occur during this deterioration is obscure but such changes apparently include both oxidation and polymerization processes. The deterioration is apparently an autocatalytic phenomenon in that the products of the reaction, that is, the color bodies and/ or the sludge formed, serve to speed up or to catalyze the further deterioration of the oil itself. The prior attempts made to prevent this deterioration of lubricating and transformer oils concerned themselves with the use of oxidation inhibitors or anti-oxidants.

This invention particularly relates to the use of substances or compounds which'apparently are not oxidation inhibitors but instead are retarders of the polymerization effect or reaction. It has been found, furthermore, that metallic naphthenates or metallic salts of organic acids naturally occurring in petroleum oils are vastly superior for the purpose of stabilizing lubricating and transformeroils than any of the other substances used for similar or analogous purposes. These metallic naphthenates or metallic salts of naturally occurring petroleum acids should preferably be oil-soluble.

It is also an object of this invention to dis-' close and provide a method whereby metallic salts of naphthenic and other naturally occurring petroleum acids, particularly suitable for the purposes of this invention, may be readily prepared.

It is an object of this invention to disclose and provide a petroleum oil capable of resisting deterioration such as normally results from the exposure of petroleum oils to the effect of light and/ or air. 7

Another object is to disclose and provide a lubricating or transformer oil which maintains its stability for prolonged periods of time without the precipitation or formation of carbonaceous material and/or sludge.

Another object of this invention is to disclose and provide a transformer oil capable of maintaining its color and dielectric strength upon exposure to light and/or air.

A still further object of this invention is to disclose and provide a petroleum oil containing a metallic salt of a naturally occurring acid in quantity 'sufficient'to stabilize the oil against deterioration caused by exposure of the oil to light and/or air without materially affecting the viscosity of the oil.

Another object of this invention is to disclose and provide a petroleum oil containing metallic salts of naphthenic acids, the oil being resistant to deterioration upon exposure to light and/or air.

An object of this invention is to disclose and provide a petroleum lubricating or transformer oil containing a substance capable of retarding and/or inhibiting the polymerization reaction or efi'ect normally produced in such lubricating or transformer oils upon their exposure to light and/ or air.

A still further object of this invention is to disclose and provide a mode of preparing metallic salts of naturally occurring petroleum acids such as naphthenic acids, whereby metallic salts particularly adapted for the purposes of this invenmetallic salts of those organic acids which occur naturally in petroleum oils.

These organic petroleum acids are commonly known as naphthenic acids and are obtained from crude petroleum lubricating oil distillates, before acid'treatment, by treating the distillates with caustic sodaor other suitable alkali solutions, extracting the sodium salts of the acids with water, and then acidifying the wash water,'whereup on the organic petroleum or naphthenic acids rise to the surface and maybe skimmed oif. Preferably these crude acids are purified and metallic salts made therewith for use in accordance with this invention. The naphthenic acids obtained from petroleum lubricating oil distillates in this manner may vary in viscosityand in molecular weight according to the particular distillate from which they are derived, and it is to be understood that they may not consist solely or entirely of true naphthenic acids, properly so-called, but for pur-- poses of simplicity reference will hereinafter be made to these acids as naphthenic acids. It has been found that these acids are suitable for the preparation of the metallic salts used as stabilizers even though they are not theoretically pure naphthenic acids. Furthermore, it has been found that naphthenic acids derived from any source whatever may be used in place of the acids obtained as described hereinabove.

A great variety of metallic salts of these naphthenic acids produce suitable stabilizers. It is desirable, however, that the metallic salt of naphthenic acid be oil-soluble and not of an undesirable color, that is, not impart an undesirable color to the oil. It has been found that among the metals whose naphthenic acid salts provide suitable stabilizers are calcium, manganese, lead, zinc. copper, cobalt, sodium, potassium and others. The calcium salt appears to be commercially best suited for this purpose in view of its low cost of preparation, lack of undesirable color, and high effectiveness.

In general, the increase in stability imparted to the refined lubricating and transformer oils by the addition of these metallic naphthenates appears to increase with the amount of naphthenates added. It is not desirable, however, to employ more than about 2% by weight of the metallic naphthenate because of the adverse ef-' fect of larger amounts. For example, the viscosity of the oil is slightly increased. by the addition'of the naphthenates, the increase in viscosity being measurable with amounts over about 0.25 while more than 2% of a'metallic naphthenate produces a product approaching a greasing consistency. The amount of the stabilizer to be added to an oil will var; with the particular metallic naphthenate and the particular lubricating and/or transformer oil to be stabilized, but in general it has been found that from about 0.1%.to 2.0% of naphthenate will give the desired results. Y

The preferred method of producing naphthenic acids and metallic naphthenates suitable for the purposes of this invention maybe prepared in accordance with the following illustrative example: a straight run lubricating oil distillate having a viscosity of about 640 seconds Saybolt at F. was washed before acid treatment with. an aqueous caustic soda solution. The alkaline wash water (containing some distillate and the sodium salts of the naphthenic acids) wasextracted with a light mineral oil solvent such as gasoline, to remove the small amounts of raw hydrocarbon distillate present.

After separation of the immiscible layers, the alkaline solution (containing the sodium salts of the naphthenic acids) was acidified with a dilute mineral acid such as sulfuric, so as to liberate the petroleum or naphthenic acids which rose to the surface and were skimmed off. These naphthenic acids were then distilled to remove the light mineral oil solvent and were again dissolved in a dilute caustic soda solution. Although sodium or potassium naphthenates may beemployed as stabilizing agents of lubricating and transformer oils, it is preferable to employ the salts of the heavier metals such as calcium, manganese, zinc, lead, aluminum, etc. For this reason, an aqueous solution of the heavier metallic salt whose naphthenate is desired, such as for example an aqueous solution of calcium chloride, manganese chloride, the solution of sodium naphthenates and a waterinsoluble metallic naphthenate thus precipitated,

This precipitated water-insoluble metallic naphthenate is then washed substantially free of excess alkali by agitation with water and then separated from the aqueous phase by decantation, filtration, centrifuging, or in any other suitable manner.

It is important that the metallic naphthenates to be used as stabilizers be substantially free of lubricating distillate hydrocarbons as such lubricating distillate hydrocarbons are generally unstable to light and air and would contaminate the refined lubricating oils or transformer oils in which the metallic naphthenates are to be used as stabilizers.

If the lubricating or transformer oil to be stabilized is of a relatively light color, then the purified naphthenic acids (liberated from the alkaline solution by acidification, as described hereinabove) are preferably redistilled at a reduced pressure. In this manner, lighter colored naphthenates are formed upon subsequent precipitationof the metallic salts, these lighter colored naphthenates not affecting the initial color of the lubricating or transformer oils to which they may be added.

The oil-soluble metallic naphthenates prepared as described hereinabove, are then incorporated into a refined lubricating, transformer or switch oil by being dissolved therein in the proper proportions of between about 0.05% to 2.0%. For most purposes, from about 0.05% to 0.2% of the metallic naphthenate is sufficient to effectively stabilize the oil. Heating of the oil facilitates the solution of the naphthenates therein but such heating is not necessary.

Illustrative of the stabilizing effect of the metallic naphthenate compounds, attention is called to the following table which shows the results obtained by adding 0.1% by weight of various metallic naphthenates, prepared as above described, to a refined California red oil of 60 seconds Saybolt at 210 F. (about 700 seconds Saybolt at etc., is then added to In other words, this refined red oil without the addition of any of these stabilizing naphthenates, precipitated an insoluble gummy material upon exposure in glass to sunlight and air for 7 days; The same oil containing 0.1% of a metallic naphthenate exposed in glass to sunlight and air did not exhibit or precipitate an insoluble gummy material for from 44 to 63 days. Manganese naphthenate was apparently most effective, delaying the precipitation of the carbonaceous or gummy material for 63 days.

As has been stated hereinabove, the amount of the stabilizer influences the degree of stabilization obtained. When, for example, the untreated lubricating oil requires '7 days for the appearance of a precipitate, 0.05% of calcium naphthenate added to such an oil will prolong this period of time to 31 days before a precipitate is observed. An increase in the quantity of calcium naphthenate to 0.10% will result in an oil requiring 52 days exposure to light and air before the appearance of a precipitate. Similarly, whereas 0.05% of lead naphthenate produced an oil which was stable for 29 days, the same oil containing 0.10% of lead naphthenate was stable for 45 days. As the increase in the quantity of metallic naphthenate has a tendency to increase the viscosity of the oil, it is not desirable toemploy more than about 2% of the metallic naphthenate in lubricating or transformer oils.

In addition tolthe inhibition of the sludge and the retardation of the polymerizing effect, the metallic naphthenates stabilized the color of the oil. Generally, there is always a marked deterioration in color before the appearance of the gummy precipitates referred to hereinabove. In the following table the effect of acalciumnaphthenate on three diflerent oils is shown. The colors there reported on the two lubricating oils were with a Tagliabue-Robinson colorimeter on which the darker colors are represented by smaller numbers. The colors taken on the transformer oil were with a Saybolt chromometer, the darker colors being represented by smaller numbers.

e? east stabilizer thenate Liibricating oil, 706 secs. Saybolt sit-100 '(a) Color at start 9 9 (b) 0010: after 21 days 8% 9% Luibricating oil, l10 secs. Saybolt lit-100 '(a) Color at start 11%; 11%

(b) Color after 7 days 9 4 13% Ttfn nsiormer oil, 52 secs. Saybolt at--l 'a) 00101- at am Plus Plus 1 ((2) Color alter 7 days 4 1 presence of the stabilizing agent added. It will also be noted that the color of the very highly refined transformer oil was initially darkened by the addition of the metallic naphthenate,

but that at the end of the I days, the color of the stabilized oil was higher than that of the unstabilized oil.

. The viscosity of the crude lubricating oil distillate from which'the naphthenic acids are obtained has little or no effect on the stabilizing power of the metallic naphthenates prepared from them. For example, calcium naphthenates were prepared, in one case from naphthenic acids obtained from a California lubricating oil distillate having a viscosity of 100 F. of 39 seconds Saybolt and in another case from a distillate having a.viscosity at 100 Ref 640 seconds Saybolt. These two calcium naphthenates were compared by'dissolving 0.1% by weight of each in a California refined lubricating oil having a viscosity of 60 seconds Saybolt at 210 F. and a color of 9%, Tagliabue-Robinson. In each case the color of the oil dropped to 9 Tagliabue-Robinson after exposure to light and air for 28 days, whereas the same refined oil without the addi tion of any stabilizing agent darkened to a color of 0 Tagliabue-Robinson in the same period of time.

As pointed out above, purification of. the crude naphthenic. acids by thorough removal of lubricating oil distillate is necessary, as this distillate is unstable to light and air and would contaminate the lubricating oils in'which the metallic naphthenates are used as stabilizers. Salts precipitated from the alkaline wash watersafter acid treatment of the lubricating oil distillates are not suitable for the preparation of these metallic naphthenates, due to the formation of sulfonic acids,- etc., in the sulfuric acid treatment, and the contamination of the naphthenates with sulfonates, .etc. The naphthenates should be substantially free from sulfonates and/or sulfonic acids, that is, they should contain sulfonates in negligible and inconsequential quantities only.

It will be obvious to those skilled in the art from the description given hereinabove that this invention discloses a method of stabilizing refined lubricating, transformer and switch oils whereby their life is extended from seven to nine times the life of an unstabilized oil, without the introduction of any ingredients which would in any way be detrimental or impair the physical properties of the product. Furthermore, the stabilizing agents are easily obtainable and inexpensive.

A mode of extracting and purifying the naphthenates has been described in detail but those skilled in the art will observe that numerous changes and modifications could be made in the preparation or purification of the naphthenic acids and the metallic naphthenates.

All such changes and modifications as, come within' the scope of the appended claims are embraced thereby.

I claim:

1. A stabilized mineral oil containing a calcium naphthenate in amounts of between about 0.05% and 2.0%.

2. A stabilized petroleum lubricating or transformer oil containing a metallic naphthenate from the group consisting of calcium, manganese, led, zinc, coppenaluminum and cobalt naphthenates in amounts of between about 0.05%

and 2.0% and in amountinsufiicient to materialtransformer oil and electric switch oil. characterized by its resistance to change in color and to deterioration when exposed to light and air, containing a metallic naphthenate from the group consisting of calcium, manganese, lead, zinc, copper and cobalt naphthenates, said metallic naphthenate being present in amount of between 0.05% by weight and an amount insufficient to materially increase the viscosity of the mineral oil and impart stringiness thereto but not exceeding 2%.

7. A stabilized liquid petroleum lubricating or transformer oil containing an oil soluble metallic naphthenate in amounts of between about 0.05 percent and 2.0 percent and in amount insufllcient to materially increase the viscosity of the refined petroleum oil.

8. A stabilized liquid petroleum lubricating or transformer oil containing a refined petroleum oil and an oil soluble metallic naphthenate from the group consisting of calcium, manganese, lead, zinc, copper and cobalt naphthenates, said oil soluble naphthenate being present in amounts not greater than 2 percent by weight.

CHARLES K. PARKER. 

